Improving community spate irrigation

Spate irrigation is an ancient form of water management, involving the diversion of flashy spate floods running off from mountainous catchments, using simple deflectors of bunds constructed from sand, stones and brushwood on the beds of normally dry wadis. Flood flows, usually flowing for only a few hours with appreciable discharges, and with recession flows lasting for only one to a few days, are channelled through short steep canals to bunded basins, which are flooded to depths of 0.5 m or more. Subsistence crops are planted only after irrigation has occurred. Crops are grown from one or more irrigations using residual moisture stored in the deep alluvial soils formed from the sediments deposited from previous irrigations. Due to unpredictable numbers, timing and volumes of floods, this type of agriculture is very risk-prone and requires high levels of co-operation between farmers to divert and manage the distribution of flood flows. At present little guidance is available to development agencies, irrigation departments, Non-Governmental Organisations (NGOs) and consultants concerned with improving or developing spate systems. These guidelines are a first step towards improving this situation, by describing the strengths of traditional systems, and the approaches that have resulted in both successful and unsuccessful spate irrigation improvement projects. These guidelines are organised around chapters containing summary descriptions of the various aspects of spate irrigation that are considered, usually with the aid of some specific examples. Recommendations for improving existing spate schemes, and developing spate irrigation in new areas, are made in Chapter 12 of the report.